In aqueous electrochemical systems such as batteries, fuel cells, and reactors for production of chemical products there exists a need to provide a cathode which will optimize reduction of peroxyl ions or dissolved chlorine or oxygen at the cathode. Examples are those batteries or fuel cells in which the cathode reaction is the electrochemical reduction of chlorine or peroxyl ions and also air depolarized chlorine electrolysis cells in which reduction of oxygen from air occurs at the cathode while chlorine is evolved at the anode.
It is a general rule that the cathode electrode should be chemically and electrochemically inert; that is, it should not corrode to any significant extent and, at the same time, it should permit the electrochemical reduction reaction to occur with the lowest possible driving potential. In alkaline solution, a typical reduction may be that of peroxyl ions. This reduction should occur at high rates at an electrode potential as close as possible to that which is observed when the rate is very low; in other words, little polarization should be manifested. For this description, low rates are about 0-10 mA/cm.sup.2 of electrode surface and high rates are greater than 100 mA/cm.sup.2. Heretofore, preferred state-of-the-art electrode materials for this type of operation have been colloidal black platinum electrodeposits and palladium electrodeposits on an inert substrate. It is generally found, however, that when dealing with peroxyl ion and chlorine and oxygen reductions their electrochemical behavior is unpredictable. In clean electrolyte they show very little polarization at high rates but they are easily "poisoned" by impurities in the solution. The poisoning is manifested by an increase in polarization especially at high rates. The polarization may be as great as one to two volts but it is more frequently of the order of 0.1-0.2 volts. Typical poisons which inhibit the electrochemical reaction are chloride ions, sulfides, cyanide, mercury, and certain organic compounds such as amines. This topic is discussed with particular emphasis on platinum cathodes in the book "Catalysis" by S. Berkman, J. C. Morell, and G. Egloff, page 398, published in 1940 by Reinhold Publishing Corp., New York, N.Y.